1. Field of the Invention
The present invention relates to a WiMax/WiBro system, especially to a method for forwarding direct message in a partial function OFDMA relay system.
2. Description of the Related Art
In a WiMax/WiBro system, in order to save the cost, some RSs are designed to consist of only a RF module and a DFT/IDFT module and no modulation/demodulation module and encoder/decoder module. This RS is called a partial function RS (PFRS). FIG. 2 shows comparison of function modules between the partial function RS and a conventional full function RS (FFRS). Because of the omission of the modulation/demodulation and the encoder/decoder, the PFRS not only saves more cost than FFRS, but also the performance in delay of message forwarding is greatly improved in PFRS.
In a relay WiMax/WiBro system, direct message forwarding (DMF) is an important approach that makes full use of spectrum resource to improve the throughput and reduce the delay. The principle of direct message forwarding is illustrated in FIG. 3.
In FIG. 3a, a conventional process of message forwarding when two users within the same RS are in communication in a relay system is illustrated, i.e., the message is forwarded from user 1→RS 1→BS→RS 1→user 2. This conventional message forwarding method greatly wastes resources. To save the resource and improve system throughput, the DMF directly forwards the message to user 2 with no help of BS, as shown in FIG. 3b. 
Because of lack of modulation and encoder modules in the partial function RS, the direct message forwarding can not be implemented with any existing method so that performance improvement resulted from direct message forwarding can not be realized.
In detail, the solution of existing DMF is as follows:                i) User 1 initiates a connection request;        ii) RS 1 receives the connection request for the user and determines a requested destination user, i.e., to determine whether user 2 is within its coverage or not. If yes, goes on iii˜vii, otherwise, goes on ix˜xv, that is, the conventional establishing flow for connection;        iii) RS 1 sends a connection indication to user 2;        iv) User 2 sends the connection responds to RS 1;        v) RS 1 sends a connection ACK to user 1;        vi) RS 1 sends a connection notification to the BS, informing it of a state of the established connection;        vii) After receiving this connection notification, the BS begins to charging;        ix) RS 1 forwards the connection request to the BS;        x) The BS sends a connection notification to the RS where user 2 locates, i.e., RS 2;        xi) RS 2 forwards the connection notification to user 2;        xii) User 2 sends a connection response to RS 2;        xiii) RS 2 forwards the connection response to BS;        xiv) BS sends a connection ACK to RS 1;        xv) RS 1 forwards the connection ACK to user 1.        
The PFRS may not decode the connection request, so what it can do is to implement step ii (to determine whether the request destination user is within its coverage or not), step iii (to send a connection indication to user 2) and so on. Therefore, PFRS has no idea in direct message forwarding.